Filter dyes in photographic elements may be in various locations in an element. They may be in a radiation-sensitive layer, in an overcoat layer, in a layer adjacent to the radiation-sensitive layer, in an interlayer in a multilayer element, in an undercoat layer adjacent to the support or in a backing layer on the side of the support opposite the radiation-sensitive layer.
Filter dyes that function primarily to absorb unwanted radiation due to reflection or refraction from layer interfaces, the layer-support interface, and particularly from the back side of the support, are referred to as antihalation dyes. The layers that contain them are referred to as antihalation layers.
It is usually important that the filter dyes in photographic elements not wander from the layer in which they are incorporated, during or after coating. It is also almost always important that the dye be easily and completely bleached or otherwise removed from the element during processing, and not be regenerated. This requirement is important since residual dye in the coating is a source of objectionable stain.
The problem of dye stain is exacerbated by trends in the photographic industry to systems with very short processing times. Shortened processing times in, for example, x-ray and microfilm processing systems, necessitate shortened wash times, which mean less time for dye removal.
Mordants are often used to prevent filter dyes from wandering to other layers. Mordants, however, work against the aim of shortening processing times and elimination of dye stain. Therefore, mordants that prevent wandering but effectively release the dye during processing are highly desirable.